1. Field of the Invention
The present invention relates to a high speed direct mold clamping apparatus, more particularly, in which a grooved channel for the flow of oil is formed inside a clamping cylinder so that the clamping ram can perform high speed reciprocation in the clamping cylinder.
2. Background of the Related Art
An injection molding machine includes an injection apparatus for injecting molten resin into a mold and a mold clamping apparatus for pressing a mold not to be open during injection and cooling.
The mold clamping apparatus opens/closes a first mold attached to a moving platen with respect to a second mold installed in a stationary platen, and exerts clamping force to the closed mold. Such mold clamping apparatuses are classified into a toggle-type, a direct pressure type, a mechanical locking type and so on. The direct pressure type or direct mold clamping apparatus drives a clamping ram under the hydraulic pressure generated from a clamping cylinder to shift a moving platen and apply clamping force to the mold.
FIG. 1 is a side sectional view illustrating a conventional direct mold clamping apparatus of an injection molding machine. As shown in FIG. 1, a conventional direct mold clamping apparatus of an injection molding machine includes a clamping cylinder 100, a clamping ram 110 slidably coupled with the clamping cylinder 100 and having a column-shaped booster cylinder 112 therein, a moving platen 120 fixed to one end of the clamping ram 110 and having a moving mold 122 attached thereto, a stationary platen 130 fixed opposite to the moving platen 120 and having a stationary mold 132 attached thereto, a plurality of tie bars 140 coupled with the moving platen 120 and stationary platen 130 and for guiding the moving platen 120, a booster ram 150 slidably coupled with the booster cylinder 112 of the clamping ram 110 and fixed to the clamping cylinder 100 and a prefill valve 160 movably installed in one end of the clamping cylinder 100 to open/close the port 104.
The clamping cylinder 100 has first to fourth ports 102, 104, 106 and 108 for allowing the flow of oil. The first port 102 is connected with the booster ram 150 fixed to the clamping cylinder 100, the second port 104 is leaded into the clamping cylinder 100, the third port 106 is connected with the prefill valve 160 for opening/closing the entrance of the second port 104 connected with the clamping cylinder 100, and the fourth port 108 is leaded into the clamping cylinder 100 at the other portion of the clamping ram 110. A channel 151 is formed inside the booster ram 150 in a longitudinal direction of the booster ram 150.
The operation of the direct mold clamping apparatus will be described in conjunction with the drawings as follows.
FIG. 2A is a side sectional view illustrating the mold clamping apparatus shown in FIG. 1 in which the mold is opened, FIG. 2B is a side sectional view illustrating the mold clamping apparatus shown in FIG. 1 in which the moving platen is advancing forward, FIG. 2C is a side sectional view illustrating the mold clamping apparatus shown in FIG. 1 in which the mold is closed, and FIG. 2D is a side sectional view illustrating the mold clamping apparatus shown in FIG. 1 in which the moving platen is returning.
As shown in FIG. 2A, the mold clamping apparatus in the initial position has the moving platen 120 detached from the stationary platen 130.
As shown in FIG. 2B, the moving platen 120 fixed to the clamping ram 110 moves toward the stationary platen 130 to close the molds 122 and 132 where molten resin are discharged. In this stage, oil is introduced through the first port 102, and flows into the booster cylinder 112 through the channel 151 in the booster ram 150. Then, oil in the booster cylinder 112 presses the clamping ram 110 to move within the clamping cylinder 100. As a result, the moving platen 120 coupled with the clamping ram 110 is shifted toward the stationary platen 130. As the clamping cylinder 100 is vacuumized in response to the movement of the clamping ram 110, oil is introduced from an external oil tank through the second port 104 leaded into the clamping cylinder 100.
As shown in FIG. 2C, when the moving platen 120 arrives at the stationary platen 130 thereby closing the mold, high pressure oil is fed through the third port 106. Oil fed through the third port 106 presses the prefill valve 160 to shift the same closing the second port 104. In a position that the second port 104 is closed, high pressure within the clamping cylinder 100 induced by the oil through the channel in the prefill valve 160 make the moving platen 120 coupled with the clamping ram 110 apply clamping force to the molds 122 and 132.
As shown in FIG. 2D, after completing a injection and cooling, feeding oil through the first and third ports 102 and 106 is stopped. At the same time, when high pressure oil is flown through the fourth port 108 into the clamping cylinder 100, the prefill valve 160 retreats to open the second port 104 and shift the clamping ram 110 backward. As a result, oil is returned from the inside of the clamping cylinder 100 via the first to third ports 102, 104 and 106 to the original storages.
However, the conventional mold clamping apparatus has a problem of complicated structure owing to the prefill valve 160 and the ports 102 and 106 for operating the prefill valve 160, which in turn raises the cost of the mold clamping apparatus.
Further, when the clamping ram 110 is advancing forward, negative pressure within the clamping cylinder 100 introduces oil from the external oil tank. However, the suction of oil via the negative pressure shakes the oil level in the oil tank, which causes error in the control of oil.
FIG. 3 is a side sectional view illustrating a conventional mold clamping apparatus with a closed channel. As shown in FIG. 3, the conventional mold clamping apparatus is characterized in that holes 202 and 204 are formed at both sides inside a clamping cylinder 200 where a clamping ram 210 reciprocates and a closed channel 205 is formed within an inside wall of the clamping cylinder 200 to connect the holes 202 and 204. Therefore, oil is discharged from the clamping cylinder 200 through the hole 204 at one side of clamping cylinder 200 which the clamping ram 210 approaches when the clamping ram 210 moves within the clamping cylinder 200, and then introduced into the clamping cylinder 200 through the hole 202 at the other side. That is, when the clamping ram 210 performs reciprocation, oil in the clamping cylinder 200 forms a course that circulates within the clamping cylinder 200.
In the mold clamping apparatus having the closed channel 205, the clamping ram 210 can rapidly move within the clamping cylinder 200 because oil does not flow between the clamping cylinder 200 and the external oil tank when the clamping ram 210 reciprocates within the clamping cylinder 200.
However, it is necessary to limit the size of the channel 205 according to the size of the clamping cylinder 200, and the channel 205 of the limited size also restricts the quantity of oil flowing therethrough, so that the clamping ram 210 cannot reciprocate at high speed.
Further, the clamping cylinder 200 has a large volume because the channel 205 is formed within the inside wall of the clamping cylinder 200, and it is difficult to fabricate the clamping cylinder 200 since the clamping cylinder 200 has an asymmetric shape to form the channels 205. Moreover, it is also difficult to form the channel 205 in the clamping cylinder 200 that has the machined inside.
FIG. 4 is a side sectional view of a conventional mold clamping apparatus having a clamping cylinder of stepped inside diameter sections. As shown in FIG. 4, the conventional mold clamping apparatus is characterized in that a large diameter section 302 of a first length K1 and a small diameter section 306 of a second length K2 are discriminatively formed inside a clamping cylinder 300 where a clamping ram 310 reciprocates. In an piston head 312 of the clamping ram 310, an O-ring 314 is installed to shut the small diameter section 306 of the clamping cylinder 300 from the large diameter section 302 of the clamping cylinder 300. The inside diameter of the large diameter section 302 is formed larger than that of the small diameter section 306, and the inside diameter of the small diameter section 306 is substantially same as the outer diameter of a piston head 312 of the clamping ram 310.
When the clamping ram 310 moves from the large diameter section 302 to the small diameter section 306 within the clamping cylinder 300, oil flows from the small diameter section 306 beyond the piston head 312 in a direction reverse to the motion of the clamping ram 310.
However, the O-ring 314 installed in the piston head 312 of the clamping ram 310 and made of for example rubber is expanded in the large diameter section 302 of the clamping cylinder 300 but is compressed in the small diameter section 306 owing to the movement of the clamping ram 310. Also, there is a step 307 between the large diameter section 302 and the small diameter section 306 of the clamping cylinder 300. Therefore, as the clamping ram 310 repeatedly reciprocates between the large diameter section 302 and the small diameter section 306, the O-ring 314 collides against the step 307 at the side of the small diameter section 306, potentially tearing itself.
When the piston head 312 of the clamping ram 310 which moves with high speed is located in the large diameter section 302, the piston head 312 does not contact the inner surface of the large diameter section 302. Thus, radial vibration may take place in the clamping ram 310 when the clamping ram 310 reciprocates at high speed. If a guide 320 supporting a front portion of the clamping ram 310 is extended longitudinally to prevent the vibration, the stroke length of the moving platen is reduced, which causes difficulty in the fabrication of products with a thick mold.
Further, the piston head 312 of the clamping ram 310 is necessarily located within the small diameter section 306 when clamping force is applied. However, since it is impossible to apply the clamping force when the piston head 312 of the clamping ramp 310 is located in the large diameter section 302 owing to the thickness of the mold, it is required to increase the length of the clamping cylinder 300 in order to fabricate thick products.